Magnetic materials are used, for example, in magnetic cell memories and magnetic field sensors. In random access magnetoresistive memories, data is stored by applying magnetic fields and thereby causing a magnetic material in a cell to be magnetized into either of two possible memory states. The information stored in the memory is contained in the orientations of the magnetization vectors of the magnetic material layers used in each memory cell. Such memory cells exhibit a pronounced decrease in electrical resistance when an applied magnetic field brings the magnetization vectors in different layers into alignment. Recalling data is accomplished by sensing resistance changes in the cell. The cells can be written or erased by applying magnetic fields created by passing currents through conducting lines external to the magnetic structures, or through the magnetic structures themselves.
There are often undesirable magnetic fields in and about the device, which are generated either as part of the device operation or from external sources. Such fields can have significant effects on the magnetization of the magnetic thin film. The field can contribute to a loss of information or to storage of erroneous information in the magnetic memory cells. Thus, magnetic memory cells function best when they are protected from external magnetic field disturbances.
A metal with a relatively high magnetic permeability can be used to form a shield for protection from magnetic fields. Metals that are used widely in magnetic shielding include soft magnetic or high permeability materials, such as NiFe, NiFeMo and NiFeCu. Such magnetic shielding materials, are generally available from metal supply companies, such as Carpenter Technology Corporation of Wyomissing, Pa.
U.S. Pat. No. 5,939,772 entitled “Shielded Package For Magnetic Devices,” issued Aug. 17, 1999, describes the use of magnetically permeable metal shields attached to the outside of a hermetically sealed ceramic package. The shields are electrically connected to the package ground plane. Laminated magnetic shielding for ceramic packages is also described in U.S. Pat. No. 5,561,265, issued Oct. 1, 1996.
Ceramic package technology can be expensive. Furthermore, as performance increases, the physical characteristics of ceramic packages may become limiting. Specifically, a ceramic material based on Al2O3 has a relatively high dielectric constant (∈r˜7-8). Additionally, because of the high-temperature processing, metallization is limited to refractory metals that are quite resistive, such as Mo and W.
Other references include application of magnetic shielding within a plastic package. U.S. Pat. No. 4,953,002, issued Aug. 28, 1990, for example, teaches magnetic shielding internal to a plastic encapsulated package.
Magnetic integrated circuit structures must also be housed in a way that minimizes cost if they are to be viable for the commercial memory market. Therefore, a shielding arrangement to protect magnetic films in magnetic integrated circuit structures from significant external adverse influences, including external magnetic fields, and which can be provided economically, would be desirable. Desirably, such a shielding arrangement should be flexible enough to meet the varied needs of integrated circuit users.